Starch consists of a mixture of amylose (15-30% w/w) and amylopectin (70-85% w/w). Amylose consists of linear chains of α-1,4-linked glucose units having a molecular weight (MW) from about 60,000 to about 800,000. Amylopectin is a branched polymer containing α-1,6 branch points every 24-30 glucose units; its MW may be as high as 100 million.
Sugars from starch, in the form of concentrated dextrose syrups, are currently produced by an enzyme catalyzed process involving: (1) liquefaction (or viscosity reduction) of solid starch with an α-amylase into dextrins having an average degree of polymerization of about 7-10, and (2) saccharification of the resulting liquefied starch (i.e. starch hydrolysate) with amyloglucosidase (also called glucoamylase or GA). The resulting syrup has a high glucose content. Much of the glucose syrup that is commercially produced is subsequently enzymatically isomerized to a dextrose/fructose mixture known as isosyrup. The resulting syrup also may be fermented with microorganisms, such as yeast, to produce commercial products including ethanol, citric acid, lactic acid, succinic acid, itaconic acid, monosodium glutamate, gluconates, lysine, other organic acids, other amino acids, and other biochemicals, for example. Fermentation and saccharification can be conducted simultaneously (i.e., an SSF process) to achieve greater economy and efficiency.
α-Amylases hydrolyze starch, glycogen, and related polysaccharides by cleaving internal α-1,4-glucosidic bonds at random. α-Amylases, particularly from Bacilli, have been used for a variety of different purposes, including starch liquefaction and saccharification, textile desizing, starch modification in the paper and pulp industry, brewing, baking, production of syrups for the food industry, production of feedstocks for fermentation processes, and in animal feed to increase digestability. These enzymes can also be used to remove starchy soils and stains during dishwashing and laundry washing.
Several Aspergillus species, including A. clavatus, show strong amylolytic behavior, which is retained under acidic conditions. See Nahira et al. (1956) “Taxonomic studies on the genus Aspergillus. VIII. The relation between the morphological characteristics and the amylolytic properties in the Aspergillus,” Hakko Kogaku Zasshi 34: 391-99, 423-28, 457-63. A. clavatus, for example, secretes an amylase activity among other polysaccharide-degrading enzymes, which allows this fungus to digest complex carbohydrates in its environment. See Ogundero et al. (1987) “Polysaccharide degrading enzymes of a toxigenic strain of Aspergillus clavatus from Nigerian poultry feeds,” Die Nahrung 10: 993-1000. When the effect of pH on the ability of A. clavatus to degrade milled feedstuff was determined, A. clavatus was shown to degrade feeds over all the tested pH values from 3.2 to 7.8. See Ogundero (1987) “Toxigenic fungi and the deterioration of Nigerian poultry feeds,” Mycopathologia 100: 75-83. Later studies showed peak A. clavatus amylase activity at pH 7-8, when the A. clavatus were grown on maize yeast extract medium or wheat yeast extract medium. Adisa (1994) “Mycoflora of post-harvest maize and wheat grains and the implications of their contamination by molds,” Die Nahrung 38(3): 318-26.